It is known that modern engines are provided with one or more exhaust after-treatment devices. The after-treatment devices may be any device configured to change the composition of the exhaust gases, such as a diesel oxidation catalyst (DOC) located in the exhaust line for degrading residual hydrocarbons (HC) and carbon oxides (CO) contained in the exhaust gas, and a diesel particulate filter (DPF) located in the exhaust line downstream the DOC, for capturing and removing diesel particulate matter (soot) from the exhaust gas
In particular, the diesel particulate filter collects liquid and solid particles in a porous substrate structure, while allowing exhaust gases to flow through. As it reaches its nominal storage capacity, needs to be cleaned by a process called regeneration. During such regeneration process, the exhaust gas temperature is increased, by means of late fuel injections, to create a condition whereby the pollutants, which have been accumulated in the filter are burned, i.e. oxidized. The process includes a closed-loop control typically on the DPF upstream temperature in order to maintain adequate temperatures in the exhaust line, optimizing the event against component drifts and ore external noises. Hereafter, with exhaust gas temperature at the particulate filter inlet (or, exhaust gas temperature at DPF inlet) will be intended the DPF upstream temperature, wherein for temperatures in other locations along the exhaust pipeline, we will refer as exhaust gas temperature.
Actual control strategies of the exhaust gas temperature at DPF inlet are mainly based on the engine working point, that is to say, one or more calibrated maps, based on engine speeds and loads are used. This means that such control strategies are not completely accounting for any exhaust gas physical change: exhaust gas mass flowrate, temperature and pressure. Since all these parameters are strictly connected to the dynamic response of the system, a control which is not based on them cannot optimize the trade-off between calibration effort and performances of the exhaust system.
In fact, the time response of an exhaust system, including a DOC or LNT device, when thermal stimulated through late injection quantities, is mainly related to the gas mass flowrate, gas temperature in the DOC/LNT and gas pressure. In an generic exhaust line, even at fixed engine speed and load, the exhaust gas mass flowrate, temperature and pressure could be much different: for example, during transient conditions, for corrections due to different ambient conditions or to components dispersion in production. Therefore, by using a control approach not directly considering the main parameters, which affects the dynamic of the system, it is not possible to optimize the performances in terms of thermal response and let the system be robust enough, especially in transient conditions.
Therefore a need exists for a method of controlling the exhaust gas temperature at the particulate filter inlet, which not consider anymore the single engine working conditions in terms of engine speed and load, but is more based on the physical behavior of the exhaust system and its time response characteristics, and is therefore able to control the temperature in order to reach the target in a faster way, avoiding undershoot and overshoot, maximizing the regeneration efficiency and reducing the risk of catalyst aging.